Also adjust dead-tree pagination.

Also shift some forward references into footnotes.

Content:
* Document that AF can end a TL-initiated title as AU can.
* Describe AF's behavior when specified multiple times.
* Add cross references in AF, macro descriptions.
* Clarify that AT interacts with letters.
* Cross-reference LI and LE macros in all list-beginning macro
  descriptions.
* Drop explicit documentation of how some macros handle empty arguments
  are handled when this information is presented in a table; these
  already list "none", and the introduction to the "Macros" section
  explains how to explicitly pass empty macro arguments.
* When discussing "compatibility reasons", identify what we're trying to
  be compatible with (DWB mm).
* Stop reporting values of string defaults in macro descriptions; these
  are properly documented in the "Strings" section.
* Begin more macro descriptions with meaningful imperative statements.
  Stop bending into pretzel shapes trying to make these expansions of an
  abbreviation that the macro name encodes.
* Stop associating `FC` with MT memoranda; they don't use it.  (The
  internal macro `let@mt-closing` appears to be misleadingly named.)
* Explain what the second argument to `FD` does.
* Drop synopses of hook macros in favor of their descriptions in the
  in the macros that call them.  (Except for EOP and TP, which demand
  further consideration before recasting because they are called by
  traps, which aren't otherwise described.)
* Drop example from `IND` macro description; it communicated nothing
  that isn't said as well in prose.
* Document `Rf` string.
* Document `Ref` register and its use by the IND macro.

Style:
* Format macro names without leading dot.
* Recast descriptions of macros 1C, AF, AL, AT, AU, AV, AVL, BL, BS,
  BVL, COVER, COVEND, DF, DL, DS, FC, FD, FE, FS, H, HY, HZ, IA, IE,
  IND, INDP, INITI, LB, LC, LE, LI, LO, LT, MULB, ND, nP, NS, PGFORM,
  PGNH, RL, RS, SM, TL, VL, WA, and WE; and Verbnm string.
* Fix comma splice (BE).
* Parallelize wording, particularly when macros or diversions are used
  to collect input.
* Stop further indenting tables and code displays in macro descriptions.
  Aligning them with the paragraphs suffices.
* Set "none" in italics when presenting tables of parameter meanings.
* In tables, use sentences more and fragments less.
* Use more idiomatic English.
* Fix fractured wording (mine, I think) in EQ description.
* More consistently capitalize table column headings when they aren't
  metasyntactic variables.
* Fix subject/verb agreement in Le/Lf/Lt/Lx register description.

Markup:
* Use \~ instead of \space in macro synopses.
* Use \c and font alternation macros instead of \f in macro synopses.
* Use tbl(1) more idiomatically when presenting lists of strings
  available to EOP and TP macros.
* Adjust dead-tree pagination with `br` and `ne` requests.

Survey some major features to give the reader without a copy of the DWB
mm manual handy a means of entry to this huge package.

* Express requirement that an mm(7) macro be called to initialize the
  package.
* Relocate advise regarding simple mm documents earlier, and further
  simplify.

* Explicitly tell the reader how to end section heading text.
* Describe the handling of display distance in more detail.